Blowout preventer with variable inside diameter

ABSTRACT

A variable inside diameter blowout preventer capable of sealing off a bore or around an object against high well pressures, and which may be either in a ram-type preventer or an annular preventer, and wherein a plurality of anti-extrusion members are disposed for radial movement on a curved plate, either semicylindrical or annular, and so that the adjacent anti-extrusion members overlap each other from the plate radially inwardly, and the anti-extrusion members are movable as a ring or semi-circle of varying inner radius to limit or prevent extrusion of a resilient sealing member therewith when sealing with the external surface of a pipe or other object in a well bore.

imited States Patent [191 Le Rouax [4 1 July 29, 1975 BLOWOUT PREVENTER WITH VARIABLE INSIDE DIAMETER Related U.S. Application Data [63] Continuation-in-part of Ser. No. 325,529, Jan. 22,

1973, abandoned.

2,780,294 2/1957 Loomis 166/203 2,846,178 8/1958 Minor 251/229 X 3,038,542 6/1962 Loomis 166/204 3,572,628 3/1971 Jones 251/1 Primary Examiner-Martin P. Schwadron Assistant Examiner--Richard Gerard Attorney, Agent, or FirmPravel & Wilson 5 7 ABSTRACT A variable inside diameter blowout preventer capable of sealing off a bore or around an object against high [52] U S Cl 251, 277/127 well pressures, and which may be either in a ram-type [5 .Cl prevente o an annular preventer, d wherein a plu- [58] Fieid 126 127 ra1ity of anti-extrusion members are disposed for ra- 277/l29 188 2 35 166/8 dial movement on a curved plate, either semicylindrical or annular, and so that the adjacent antiextrusion members overlap each other from the plate [56] References Cited radially inwardly, and the anti-extrusion members are movable as a ring or semi-circle of varying inner ra- UNITED STATES PATENTS dius to limit or prevent extrusion of a resilient sealing Seamark member therewith when sealing the external ur- Q face of a pipe or other object in a well bore. mg 2,609,836 9/1952 Knox 277/73 12 Claims, 9 Drawing Figures u I I 1 W /7-/ K 33 J0 f f l Lllllllll'lllllll vu v uk l 33? 42 f\ g A A a //Z llllllllll lllllll a PATENTEB JUL 2 91975 SHEET PATENTEDJULZQIHYS 3.897, 038 SHEET 2 PATENTEI] JUL 2 9 i975 SHEET BLOWOUT PREVENTER WITH VARIABLE INSIDE DIAMETER CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of US. patent application Ser. No. 325,529 filed Jan. 22, I973 copending herewith, and now abandoned.

BACKGROUND OF THE INVENTION The field of this invention is blowout preventers for oil wells and the like.

Annular blowout preventers made by the Hydril Company, an example of which is shown on page 2742 of the Composite Catalog for 1970-71, have been in extensive commercial use for a number of years. Such blowout preventers provide a fully-open bore therethrough so that drill bits, reamers, casing hangers and other large diameter tools can freely pass therethrough, but when actuated to the closed position, the packing of each such preventer is forced inwardly to reduce its bore and automatically adjust its size and shape in sealing contact with whatever object happens to then be in the bore of the preventer, thereby closing off the annular space around such object to prevent a blowout of well pressure from below. If no tool is in the well, the bore of the preventer can be fully closed to prevent a blowout.

Although such Hydril blowout preventers are very satisfactory for relatively low well pressures in the range of from about 2,000 p.s.i. to 5,000 p.s.i., it is generally desirable to use a ram type blowout preventer above such pressures, and above 10,000 p.s.i. well pressure, it has heretofore been considered essential to use a ram type blowout preventer ofa predetermined opening size because of the inability to satisfactorily prevent extrusion of the rubber of the preventers at such higher pressures.

SUMMARY OF THE INVENTION The present invention relates to blowout preventers wherein a resilient sealing member or members are provided for closing a well bore or sealing with a pipe or other object disposed in the bore and wherein antiextrusion means are mounted with the sealing member or members to prevent extrusion thereof over a relatively large variable range of bore diameters for the preventer, and wherein the blowout preventers of this invention may be of the ram type or the annular type, and are yet capable of sealing off much higher well pressures than with prior known annular blowout preventers for a variable range of diameters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view illustrating a portion of one form of the blowout preventer of this invention, wherein the preventer has a pair of blowout preventer rams;

FIG. 2 is a view taken on line 22 of FIG. 1, with certain parts removed for illustration, and illustrating in particular the anti-extrusion means at the upper end of each of the rams of the blowout preventer of FIG. 1;

FIG. 3 is a sectional view taken on line 3-3 of FIG.

FIG. 4 is a sectional view taken on line 4-4 of FIG.

FIG. 5 is a sectional view taken on line 5-5 of FIG.

FIG. 6 is an isometric exploded view illustrating a pair of anti-extrusion members in the upper antiextrusion means for each of the blowout preventer rams of FIG. 1;

FIG. 7 is a view similar to FIG. 2, but illustrating the anti-extrusion members in a position in contact with a well pipe when the ram is in a sealing or closed off position around the pipe;

FIG. 8 is a vertical sectional view illustrating a modifled form of the blowout preventer of this invention which is annular and which employs the same antiextrusion members utilized in the form of the invention shown in FIGS. 1-7; and

FIG. 9 is a view similar to FIG. 8, but rotated with re spect thereto and showing the blowout preventer of FIG. 8 in the closed or sealing position with respect to a pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, the letter B refers generally to the blowout preventer of this invention (FIGS. 1-7 which is formed with a pair of rams R. The rams R are disposed in a conventional blowout preventer body or housing H having a longitudinal bore 10 therethrough, through which well pipe P or other objects such as well tools may pass in normal operations conducted with the blowout preventer B in the fully opened position, the details of which will be explained hereinafter.

Briefly, the construction of each ram R provides for a sealing with the opposite ram R and with an object such as the well pipe P which is disposed in the bore of the preventer B. By reason of the particular construction of the present invention, extrusion of the yieldable sealing means or members S with each ram R is prevented throughout a variable inside diameter range of sealing positions. An upper anti-extrusion means M and the lower anti-extrusion means M are provided for each of the rams R for preventing or inhibiting the extrusion of the sealing members S when they are in the sealing position with each other and/or with the pipe or other object P.

Considering the invention as illustrated in FIGS. 1-7 more in detail, the housing H has a lateral opening or recess 10b for each of the rams R. The ram housing H is preferably made with an upper annular flange 10c and a lower annular flange 10 d, each of which has bolt openings 10a therethrough for receiving bolts or other suitable connecting means for connecting the housing H in a stack of blowout preventers or in well casing or pipe in the known manner.

A conventional head or bonnet 12 is connected to each side of the body or housing H, and each of such heads or bonnets has a recess 12a (one of which is shown in FIG. I), and each ofwhich is aligned with the lateral openings 10b and the housing H so as to form a continuation thereof from the longitudinal bore 10. Each of the rams R is received in its respective recess 12a when in the retracted position. A piston rod 14 extends through a suitable seal 12b in the head or bonnet 12. Each piston rod 14 extends to a piston 16 of conventional construction which is disposed in a cylinder 17 having an end cap or closure 18 therewith in any known manner. For purposes of illustration, a fluid inlet line 18a is shown for introducing hydraulic fluid or other operating fluid into the cylinder 17 for moving the piston 16 inwardly towards the center of the bore 10. Another fluid line 12c is provided for introducing hydraulic fluid or other operating fluid into the cylinder 17 for moving the piston 16 outwardly (to the right as viewed in FIG. 1) to retract the ram R connected therewith. It will be understood that various power systems may be employed rather than the pistons 16 and the invention is not limited to the specific form illustrated in FIG. 1. It should also be understood that a power means such as the piston 16 shown in FIG. I is provided for the left-hand ram R as viewed in FIG. 1, in the same manner as the piston 16 illustrated for the right-hand ram R in FIG. 1.

To facilitate description, the details of only one of the rams R will be described hereinafter, and only when it is necessary to show the interaction of the two rams will the other ram be specifically identified or referred to. It will be understood that the two rams R are preferably made in the same manner so that they cooperate with each other in the sealing action on the pipe P or with each other for sealing off the longitudinal bore when it is desired to prevent a blowout of the well in which they are located.

Each ram R has a ram carrier 20 which is connected to the piston 14, preferably in the conventional releasable manner, utilizing a button 14a on the rod 14 fitting into a suitable slot in the ram carrier 20. In the preferred form of the invention, the ram carrier 20 is formed of steel or other relative rigid material and is preferably substantially semi-cylindrical in crosssectional shape and it is adapted to receive a similarly shaped semi-cylindrical seal element 21 inwardly thereof. The seal member 21 is formed of rubber or other yieldable material and it is in contact with the outer surface 11 of the sealing member S which is suitably shaped to conform with the inner surface 21a of the member 21.

The seal member 21 is confined at its upper end between the ram carrier 20 and an upper ram confining and alignment plate 24 (FIG. 1) which plate 24 is secure d to the carrier 20 by one or more cap screws 26 or other suitable securing means. It is to be noted that the upper surface 20b of the ram carrier 20 engages and slides relative to the upper surface of the recesses 10b and 12a. Similarly, the upper surface 21b of the seal member 21 engages and seals with the upper surface of the recess 10b. The upper alignment plate 24 is substantially semi-cylindrical, terminating in aligned radial ends 24a which abut with similar ends on the opposite alignment plate 24 of the other ram R when in the closed position (FIG. 1).

The ram R also has a lower ram confining and alignment plate which preferably extends for the full depth of the ram R and which has a generally semicylindrical shape at its inner portion which terminates in radial aligned end surfaces 25a which are adapted to abut with corresponding end surfaces on the opposite plate 25 of the opposite ram R when in the closed position (FIG. 1). A shoulder 25b is provided on each of the plates 25 for engagement with the carrier 20 to enable the carrier 20 to retract the plate 25 outwardly therewith but permitting inward movement of the carrier 20 relative to the plate 25 after the inward movement of the plate 25 is stopped by the engagement with the opposite plate 25 on the opposite ram R.

It is to be noted that the vertical or longitudinal area between the upper alignment plate 24 and the lower alignment plate 25 of each ram R, and inwardly of the seal member 21, forms a pocket or recess which is generally semi-cylindrical for receiving the seal member S and the anti-extrusion means M and M, which are normally the primary replaceable parts. The sealing element or member S is formed of rubber or other similar yieldable resilient material and it is adapted to be distorted or forced inwardly into sealing engagement with the external surface of the pipe P or other object disclosed in the longitudinal bore 10 of the housing H after the plates 24 and 25 of the opposite rams R have contacted each other as shown in FIG. 1.

The upper anti-extrusion means M for each ram R is identical to the lower anti-extrusion means M, except that they are upside down with respect to each other. Therefore, the details of the anti-extrusion means M will be hereinafter explained and the same parts of the lower anti-extrusion means M will be identified with the same letters and/or numerals followed by a prime mark.

The upper anti-extrusion means M is shown in detail in FIGS. 2-7 and it includes a semi-cylindrical retainer plate 33, a plurality of pie-shaped segments 35 alternately disposed with respect to a plurality of T-shaped anti-extrusion members 36. As will be more evident hereinafter, each of the segments 35 is slidably secured to the plate 33 by bolts 37 which slide radially in slots 33a of the plate 33. Each of such guide and retaining bolts 37 is threaded or is otherwise suitably secured in a threaded opening 35a of each segment 35 (FIG. 6). As best seen in FIG. 5, the head of each bolt 37 slides in an enlarged upper portion of the slot 33a so as to prevent the segments 35 from falling away from the plate 33.

The plate 33 has upstanding pins 33b disposed at several places for engagement in suitable openings in the alignment plate 24 disposed thereabove (FIG. 1). It will be understood that the semi-cylindrical shape of the plate 33 and that of the plate 24 correspond substantially to each other and the pins 33b serve to lock the plate 24 and 33 together. The ends 33c of the plate 33 are disposed radially and in alignment with each other in the same manner as the ends 24a of the alignment plate 24 thereabove. Thus, the ends 33c of the retainer plate 33 on each ram R contact and engage with corresponding ends 33c on the opposite rams R when the ends 24a reach such point of contact (FIG. 1).

Each segment 35 has a lower curved surface 35b which is preferably bonded or otherwise suitably secured to the rubber or other yieldable resilient material of the sealing member S. Each segment 35 is substantially pie-shaped and has an inner surface 350 which is arcuate in shape so that together with the other surfaces 35c, a generally circular configuration is provided for engagement with the external surface of the pipe P. Each segment 35 has an upper guide surface 35d on each side of a pointed upstanding section 35e.

Each segment 35 also has a pair of upstanding guide lugs 35f at its rear surface, each of which has an inner guide surface 35g which is substantially parallel to an inner guide surface 35h on the rear of the upstanding section 35a. The space between the surfaces 35g and 35h form a recess for receiving one leg 36a of the T- shaped anti-extrusion member 36 so as to permit lateral or circumferential movements of the T-shaped members 36 relative to the segments 35 while causing the members 35 and 36 to move together radially, as will be more evident hereinafter.

Each of the members 36 has an inner surface 361; which is preferably arcuate so that it will lie in substantially a semi-circle with the arcuate surfaces 36b of the other members 36 to facilitate contact with the external surface of the pipe P. Each segment 36 also preferably has an upstanding guide projection 36c which is adapted to extend upwardly into a recess 33d in the plate 33 to assure radial alignment and guiding of each segment 36 relative to the plate 33. To prevent the entrapment of mud or other fluid which might interfere with the radial movement of the members 36 relative to the plate 33, clearance recesses 36d are provided on each side of each member 36 and similar recesses 33e are provided in the plate 33.

It is to be noted that the end segments 135 at each end of each of the anti-extrusion means M are approximately one-half of the regular segments 35 and they otherwise function in the same manner as the segments 35.

In the operation or use of the form of the invention shown in FIGS. 1-7, the blowout preventer B is nor mally in the retracted or open position (not shown) wherein the ram carriers 20 are pulled back into the recesses 12a so that the full open bore is provided through the blowout preventer B. When it is desired to close off the bore 10 around the pipe P or even upon the rams themselves in special instances, the hydraulic fluid is introduced into the cylinders 17 to move the pistons 16 towards each other to thereby move the rams R towards each other so as to initially cause the end surfaces 24a and 25a of the plates 24 and 25 of the opposite rams R to contact each other and thus stop their inward movement. Similarly, the end surfaces 330 of the upper retainer plates 33 and the end surfaces 33'c of the lower retainer plates 33 engage each other so that their inward movement is stopped. After the inward movement of the plates 24, 25, 33 and 33' has thus been stopped, continued movement of the pistons 16 causes the ram carriers to continue their inward movement which distorts the seal members 21 and the sealing elements S radially inwardly and they ultimately move into sealing contact with the external surface of the pipe P. Since the anti-extrusion segments 35 are bonded to the sealing element S, they move radially inwardly with the sealing element S and they also carry with them the anti-extrusion members 36 in view of the interlocking relationship of the ends 36a with the lugs 35fas previously explained. As the anti-extrusion members 35 and 36 thus move inwardly with the sealing elementor member S, they contract or move circumferentially towards each other to define a smaller internal radius by the internal surfaces 35c and 36b and at all times they are disposed above the resilient material of the sealing member S. The members 35 and 36 continue their inward radial movement and also their contracting or circumferential sliding movement relative to each other until they contact the external surface of the pipe P so as to then provide a metal to metal contact between the external surface of the pipe P and the antiextrusion members 35 and 36 which inhibits or prevents longitudinal extrusion of the rubber or other yieldable material upwardly along the pipe P. The surfaces of each member 36 in contact with the surfaces 35h inhibit or prevent inward radial extrusion of the 6 rubber of the seal ring S outwardly of the members 35 and 36.

The same anti-extrusion action takes place with the lower anti-extrusion means M with the corresponding pie-shaped segments 35 and the T-shaped segments 36' so that the lower sealing means M prevents longitudinal extrusion of the rubber or other yieldable material of each sealing member 5 relative to the pipe P. Thus, the sealing member S is confined between the upper anti-extrusion means M and the lower antiextrusion means M which are in metal to metal contact with the external surface of the pipe P.

When it is desired to retract the blowout preventer B to its retracted position, the pistons 16 are moved outwardly by the introduction of hydraulic fluid or other operating fluid through the lines 12c in the known man' ner. As the ram carriers 20 are moved outwardly, the pressure on the sealing members S is relieved and by the inherent resiliency of such sealing members S they return to their retracted undistorted condition shown in FIG. 1, carrying with them the segments 35. The seg ments 36 are also retracted by the engagement of the surfaces 35h and the legs 36a so that the segments 35 and 36 continue to move as a semi-circular unit with the sealing element S during the retraction until they return to the completed retracted position (FIG. 2). 2). Thereafter, each of the rams R is moved to the fully re tracted position with the carriers 20 back into the recess 12a for each ram R, as previously explained.

In FIGS. 8 and 9, a modified blowout preventer B4 is illustrated, which is of the annular type and which may take various forms. Briefly, the preventer 13-1 includes a housing l-I-l which has a central longitudinal bore therethrough, through which a pipe P or other object is adapted to extend in the known manner for well operations. The housing I'll-1 is constructed so that it may be positioned in a stack of blowout preventers or in a string of well casing or pipe in any suitable manner, as will be well understood by those skilled in the art.

The housing H-l preferably includes a lower housing section 112 having a housing recess 112a for receiving an annular sealing element or member S-l formed of rubber or other similar yieldable resilient material as well as an upper anti-extrusion means M-1 and a lower anti-extrusion means M-1, as will be further explained. The sealing member S-1 preferably has a dished out or concave inner surface 134 (FIG. 8), the same as the inner surface of each of the sealing members S (FIG. 1), so that when the sealing member is in the sealing position with the pipe P, the rubber of the sealing mem ber and the upper and lower anti-extrusion members M-1 and M'1 are all in engagement with the pipe P, whereby extrusion of the sealing member 8-1 (or the members S in FIG. 1) is prevented. The recess 112a is further defined by a housing section or cover which is secured to the housing section 112 by bolts 115a or other suitable securing means. Fluid pressure lines 112b and 115i) communicate through the housing H-l with the recess 112a for the inlet and relief of hydraulic or other fluid pressure with respect to the resilient annular piston 114 formed of rubber or other simi-- lar material disposed in the recess 112a to control the opening and the closing of the blowout preventer B-ll, as will be more evident hereinafter. For connecting the housing H-l in a stack of blowout preventers, or to suitable flanges of the well pipe or casing above and below the preventer B-l, connecting threaded studs 112C and 115c (FIG. 9) are preferably provided, although any other suitable connecting means may be employed.

The upper anti-extrusion means M-l is identical to the anti-extrusion means M heretofore described in connection with FIGS. 1-7, except that the antiextrusion means M-l is completely circular or cylindrical so that all of the segments 35 are formed in the same manner rather than the half segments 135. The segments 35 of the anti-extrusion means M-l are bonded or are otherwise secured to the annular sealing member of ring S-1 and the segments 35 and 36 are adapted to move radially together while also moving circumferentially with respect to each other to provide for a variable inside diameter formed by the segments 35 and 36 to establish the same metal-to-metal contact with the external surface of the pipe P as heretofore described in connection with FIG. 7.

The lower anti-extrusion means M'-l is again identical to the upper anti-extrusion means M-l except that it is upside down with respect thereto so that its segments 35 are bonded to the resilient member S-l. It is also to be noted that the plate 133 for the antiextrusion means M-l is completely circular or annular rather than being semi-circular as in FIGS. 2 and 7, but it is otherwise the same. However the upstanding lugs 33b are not required with the annular plate 133. A similar annular plate 133' is provided for the lower antiextrusion means M-1 and it likewise is identical to the plate 33 except that it is annular and does not have the lugs or pins 33b.

In operation or use of the form of the invention shown in FIGS. 8 and 9, the segments 35 and the members 36 move radially inwardly and circumferentially with respect to each other as the annular piston 114 is urged inwardly by hydraulic pressure or other operating pressure introduced through the line 122!) into the recess 112a. Thus, the upper anti-extrusion means M-1 and the lower anti-extrusion means M-1 form metalto-metal contact with the external surface of the pipe P to prevent or inhibit longitudinal extrusion of the resilient yieldable material of the sealing member S-l when sealing with the pipe P. It is to be noted that such anti-extrusion effect is accomplished with different diameters of the pipe P or other objects which may be located in the well bore.

Instead of the dished out or concave surface 134 on the members S-1, or the similar surface on members 5, the shape may be modified, or recesses or the like in the members S-1 and S may be provided, the purpose of which is to compensate, or partially compensate, for the smaller volume of the space available for the rubber of the members S and S-l when in the sealing position (FIG. 9) compared to the volume available for the members S and S-l in the retracted position (FIGS. 1 and 8).

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.

I claim:

1. A blowout preventer adapted to seal with a pipe or other object in a well bore or to close same in the absence of any object in the well bore, comprising:

a resilient sealing member having an inner surface adapted to engage a pipe of the like in a well bore;

a rigid retainer plate mounted with the sealing member and having an inner surface generally conforming with the inner surface of said sealing member;

means for urging said sealing member radially inwardly relative to said inner surface of said plate for effecting a seal with a pipe or the like in a well bore or with itself for closing a well bore; and

first anti-extrusion means mounted with said plate and movable radially relative thereto in response to radial inward movement of said sealing member for preventing extrusion of the sealing member longitudinally in the area radially inwardly of said plate when fluid pressure acts on said sealing member, said anti-extrusion means including:

a first set of anti-extrusion members spaced from each other and mounted for radial movement relative to said plate;

a second set of anti-extrusion members, each mounted alternatively with respect to two antiextrusion members in said first set; and

interlocking means on said adjacent members for locking said adjacent members for radial movement together while premitting circumferential relative movement therebetween.

2. The blowout preventer set forth in claim 1,

wherein:

said plate is substantially semi-cylindrical and is adapted to be mounted as a part of a blowout preventer ram; and

said sealing member is substantially semi-cylindrical.

3. The blowout preventer set forth in claim 1,

wherein:

said plate is annular; and

said sealing member is annular.

4. The blowout preventer set forth in claim 1, including:

second anti-extrusion means mounted with said plate on the opposite side longitudinally of said sealing member from said first anti-extrusion means and movably radially relative to said plate in response to radial inward movement of said sealing member for inhibiting extrusion of the sealing member longitudinally in the area radially inwardly of said plate when fluid pressure acts on said sealing member from either longitudinal direction.

5. The structure set forth in claim 4, wherein said first and second anti-extrusion means each includes:

a first set of radially disposed anti-extrusion members circumferentially spaced from each other and mounted for radial movement relative to said plate;

a second set of radially disposed anti-extrusion members, each mounted alternately with respect to each of said anti-extrusion members in said first set; and

said anti-extrusion members in said first and second sets having overlapping surfaces, the extent of overlap of which increases as the anti-extrusion members move radially inwardly relative to said plate.

6. The structure set forth in claim 1, wherein:

said anti-extrusion members in said first and second sets having overlapping surfaces, the extent of overlap of which increases as the anti-extrusion members move radially inwardly relative to said plate.

7. The structure set forth in claim 6, wherein:

said second set of anti-extrusion members is mounted above said first set; and

said overlapping surfaces are provided by upper surfaces of each member of said first set and lower surfaces of each member of said second set.

8. The structure set forth in claim 6, wherein:

said anti-extrusion members of said first set are substantially pie-shaped; and

said anti-extrusion members of said second set are substantially T-shaped.

9. The structure set forth in claim 8, wherein:

each of said members of said first set has a recess for receiving one leg of the T" of the adjacent member of vsaid second set for circumferential sliding movements of said members relative to each other as they move radially together.

10. The structure set forth in claim 8, including:

guide means engaging said plate and each of said anti-extrusion members in said first set for guiding said members in said first set as they move radially relative to said plate; and

additional guide means engaging said plate and each of said members in said second set for guiding said members in said second set as they move radially relative to said plate.

11. The structure set forth in claim 1, wherein:

said members in said first set are bonded to said sealing member; and

said members in said second set are not bonded and are free to move relative to said sealing member.

12. The structure of claim 11 wherein:

said interlocking means comprises means on said members in said first set for engaging members in said second set for causing relative movement of said members in said second with said sealing member. 

1. A blowout preventer adapted to seal with a pipe or other object in a well bore or to close same in the absence of any object in the well bore, comprising: a resilient sealing member having an inner surface adapted to engage a pipe of the like in a well bore; a rigid retainer plate mounted with the sealing member and having an inner surface generally conforming with the inner surface of said sealing member; means for urging said sealing member radially inwardly relative to said inner surface of said plate for effecting a seal with a pipe or the like in a well bore or with itself for closing a well bore; and first anti-extrusion means mounted with said plate and movable radially relative thereto in response to radial inward movement of said sealing member for preventing extrusion of the sealing member longitudinally in the area radially inwardly of said plate when fluid pressure acts on said sealing member, said anti-extrusion means including: a first set of anti-extrusion members spaced from each other and mounted for radial movement relative to said plate; a second set of anti-extrusion members, each mounted alternatively with respect to two anti-extrusion members in said first set; and interlocking means on said adjacent members for locking said adjacent members for radial movement together while premitting circumferential relative movement therebetween.
 2. The blowout preventer set forth in claim 1, wherein: said plate is substantially semi-cylindrical and is adapted to be mounted as a part of a blowout preventer ram; and said sealing member is substantially semi-cylindrical.
 3. The blowout preventer set forth in claim 1, wherein: said plate is annular; and said sealing member is annular.
 4. The blowout preventer set forth in claim 1, including: second anti-extrusion means mounted with said plate on the opposite side longitudinally of said sealing member from said first anti-extrusion means and movably radially relative to said plate in response to radial inward movement of said sealing member for inhibiting extrusion of the sealing member longitudinally in the area radially inwardly of said plate when fluid pressure acts on said sealing member from either longitudinal direction.
 5. The structure set forth in claim 4, wherein said first and second anti-extrusion means each includes: a first set of radially disposed anti-extrusion members circumferentially spaced from each other and mounted for radial movement relative to said plate; a second set of radially disposed anti-extrusion members, each mounteD alternately with respect to each of said anti-extrusion members in said first set; and said anti-extrusion members in said first and second sets having overlapping surfaces, the extent of overlap of which increases as the anti-extrusion members move radially inwardly relative to said plate.
 6. The structure set forth in claim 1, wherein: said anti-extrusion members in said first and second sets having overlapping surfaces, the extent of overlap of which increases as the anti-extrusion members move radially inwardly relative to said plate.
 7. The structure set forth in claim 6, wherein: said second set of anti-extrusion members is mounted above said first set; and said overlapping surfaces are provided by upper surfaces of each member of said first set and lower surfaces of each member of said second set.
 8. The structure set forth in claim 6, wherein: said anti-extrusion members of said first set are substantially pie-shaped; and said anti-extrusion members of said second set are substantially T-shaped.
 9. The structure set forth in claim 8, wherein: each of said members of said first set has a recess for receiving one leg of the ''''T'''' of the adjacent member of said second set for circumferential sliding movements of said members relative to each other as they move radially together.
 10. The structure set forth in claim 8, including: guide means engaging said plate and each of said anti-extrusion members in said first set for guiding said members in said first set as they move radially relative to said plate; and additional guide means engaging said plate and each of said members in said second set for guiding said members in said second set as they move radially relative to said plate.
 11. The structure set forth in claim 1, wherein: said members in said first set are bonded to said sealing member; and said members in said second set are not bonded and are free to move relative to said sealing member.
 12. The structure of claim 11, wherein: said interlocking means comprises means on said members in said first set for engaging members in said second set for causing relative movement of said members in said second with said sealing member. 